1. Field of the Invention
The present invention relates generally to a tester for an integrated circuit and, more particularly, to a tester for a repairable integrated circuit including multiple copies of a given microcircuit.
2. Description of the Prior Art
The microelectroelectronics industry is extremely competitive. Although the general economy has been highly inflationary, price reduction has been the norm in the microelectronics industry. To succeed in the marketplace, a new product must be technologically innovative and inexpensive.
One limitation of semiconductor fabrication processes is the introduction of defects into the circuits fabricated. The active region of a semiconductor device includes the area on the surface of the device in which microcircuit elements have been fabricated. For most fabrication processes, the density of circuit elements is roughly constant and the probability of a defect being introduced into the active region of the device is proportional to the area of the active region.
Each device produced must be tested to determine whether defects in the microelectronic circuit elements fabricated in the device will adversely affect the performance of the device. A device that does not function correctly is termed a bad device. The cost of producing and testing a bad device is equal to the cost of producing and testing a good device. Therefore, the cost of a good device is determined, in part, by the percentage of the total number of devices fabricated that are good, i.e., the yield of the fabrication process. To increase yield and reduce cost, the area of the active region of the device should be small, because the probability of a device being bad increases as the area of the active region increases. However, increasing the performance of a device generally requires that the area of the active region be increased to incorporate additional circuitry.
Accordingly, the goals of increasing performance and decreasing cost impose conflicting criteria for determining the size of the active region of the device. Designers of semiconductor devices require means for increasing the amount of circuitry on a device without decreasing the yield of the device.